Mechanical integrators and control systems employing same



April 16, 1968 H M. GEYE R '7 3, 7, 7 MECHANICAL INTEGRATQRS AND CONTROL SYSTEMS 'EMPLOYING SAME Filed Jan. 3, 1966 United States Patent ABSTRACT OF THE DISCLOSURE The disclosure illustrates a mechanical integrating mechanism which algebraically sums two linear inputs and produces a fixed rotary output. A rack, which provides one linear input, engages a pinion gear mounted on a linearly displaceable trunnion mounting. The pinion gear is coupled to a fixed rotary output shaft by a fiexible coupling.

The present relates to improvements in mechanical integrators which provide .an output that is an algebraic summation of two linear inputs, and more particularly for the use of such integrators in control systems, such as a gas turbine compressor guide vane control system.

It is a common goal in the design of high performance gas turbine engines to provide for optimization of the performance of their axial flow compressors under various operating conditions. One method of achieving this end is to provide these compressors with a series of variable angle stator or guide vanes. During normal engine operation the angle of these vanes is adjusted according to a predetermined schedule, in accordance with speed, thrust, etc., to optimize the compressor performance. In doing so, particular attention is given to avoiding a condition of compressor stall.

However, under certain adverse or abnormal operating conditions, such as the ingestion of hot exhaust gases resulting from the firing of a rocket or other projectile or the actuating of a thrust reverser, compressor stall may occur if the guide vanes remain positioned in accordance with the normal schedule therefor. To avoid this condition, the angle of the guide vanes may be adjusted to restrict the fiow of gas during the period that hot gases are ingested into the compressor.

A servo system is normally employed to position the variable angle guide vanes in response to demand signals from a control unit which utilizes feedback of the actual position of the guide vanes to null out the demand signals when the guide vanes have reached their proper positions. In order to provide for momentary adjustment of the angle of the guide vanes, while at the same time avoiding redesign of the control device, the feedback signal may be modified by introducing a temporary false input which signals the controller that the guide vanes are open too far. The controller then produces a demand signal which causes a readjustment of the guide vane angle to restrict flow while hot exhaust gases are passing through the compressor.

At present a telescopic flexible cable linkage from the guide vanes to the control device provides the desired position feedback signal in this system. Introduction of the false feedback signal is accomplished by mechanism which changes the effective length of this cable in response to a signal from a device which either fires a projectile or actuates a thrust reverser. However, this approach has disadvantages in that the modified or false signal may not be accurate due to the remoteness of the telescopic joint from the control device and other complexities of the system.

One object of the present invention is to improve the performance of gas turbine engine compressors during abnormal operating conditions, especially during the ingestion of hot exhaust gases resulting from the firing of a projectile or the actuation of a thrust reverser and further, to do so using lightweight control means which are accurate in operation and simple in construction.

Another object is to provide an improved integrator adapted for use in such control systems, although not limited thereto, which has uncomplicated design, low weight and precise operation, and gives a linearly proportional output in the summation of inputs thereto.

The above objects are fulfilled by employing in a guide vane control servo system a mechanical integrator which preferably comprises two linear input members guided for rectilinear motion. A rotary integrating member engages one of said members and has relative rolling movement in response to a linear displacement thereof. The other input member is connected to said rotary integrating member and its displacement produces further rolling movement relative to said first linearly displaceable member. The rotary integrating member is coupled to an output shaft by means which rotates with said rotary member and output shaft and transmits the rotation of said rotary integrating member to said output shaft over the range of displacement of the rotary member. One input to the integrator is connected to the guide vanes and, through its output shaft, provides the desired position feedback signal. The other integrator input memher is displaced in response to an abnormal engine operating condition and introduces a false feedback signal to the output shaft of the integrator which in turn causes the guide vanes to be properly repositioned at a new reference point for the abnormal engine operating condition.

The above and other related objects and features of the invention will be apparent from a reading of the following description of the disclosure found in the accompanying drawing and the novelty thereof pointed out in the appended claims.

In the drawing:

FIGURE 1 is a block diagram showing an inlet guide vane control system in which the present invention is embodied;

FIGURE 2 is an end view, with portions broken away and in section, of a mechanical integrator used in this system;

FIGURE 3 is an elevation of this integrator with other portions in section;

FIGURES 4, 5, and 6 illustrate the motion of a coupling device of the integrator shown in FIGURES 2 and 3.

FIGURE 1 illustrates in block diagram form those portions of a control system for a gas turbine engine 10 which are employed to regulate the position of compressor guide vanes 12 (only one of which is shown) to optimize the operation of an axial flow compressor 14 normally employed in such a gas turbine engine. Pivoting of the guide vanes about a radial axis in such compressors is a well-known technique for controlling air flow, to optimize compressor operation while at the same time preventing compressor failure due to stall.

The various guide vanes 12, usually arranged in several stages, are interconnected so that they may be simultaneously pivoted (again by known means) through a mechanical connection to an actuator 16. A controller 18 comprising a computer and in part a servo mechanism (frequently incorporated in the main fuel control, not shown) establishes demand signals which feed hydraulic fluid through conduits 20 or 24 to displace the actuator 16 and move the guide vanes 12 to a desired position for the normal operating condition of the engine at any given moment. A position feedback signal is provided by a mechanical connection 26 which provides an input to an integrator 28 having an output shaft 30. The output shaft 30 transmits the feedback signal to the controller 18 and nulls out the demand signal when the vanes 12 have been pivoted to their proper positions.

The above described normal engine operation. However, there are certain conditions that cause compressor stall which cannot be conveniently provided for by the controller 18. These conditions primarily involve the temporary condition where hot exhaust gases would be ingested into the engine such as during operation of a thrust reverser or firing of missiles from an aircraft which is being propelled by the engine iii. When such a condition exists, it is necessary that the guide vanes 12 be pivoted to reduce the flow of air into the compressor. Normally the amount of closure is a predictable parameter.

In order that such a compensation in the air intake may be made, a second input is provided for the integrator 28 that may conveniently take the form of an actuator 32 which is powered by hydraulic fluid being hydraulic line 34 and controlled by a valve 36. The valve 36 is mechanically or otherwise connected to the actuator 33 for the mechanism that would cause the problem of excessive hot gas ingestion, hereinafter referred to as thrust reversal for sake of convenience. Thus when the thrust reverser is actuated, the valve 36 is opened and a second input is imparted to the integrator 28, causing a false feedback signal from the output shaft 30 to be transmitted to the controller 18. The controller 13 is automatically creates a demand signal which, through the actuator 16, pivots the guide vanes 12 to the proper position for preventing stall when an excessive amount of hot gas could be ingested.

Reference is now had to FIGURES 2 and 3 for a description of the constructional features of the integrator 28. The mechanical feedback connection 26 imparts reciprocable movement to an input member 40, which is journaled for sliding movement in a housing 42 and has secured thereto a rack 44 which meshes with a pinion 46. The pinion 46 is rotatably mounted by a shoulder screw 48 on a trunnion 59. The trunnion 59 has rods 52, 54 projecting from opposite ends and journaled in the housing 42 for movement parallel to the rack 44. A roller 56 appropriately mounted on the housing 42 provides further support for the rack 4d and maintains it in mesh with the pinion 46. In normal operation the rectilinear feedback motion of the input member 44 is transmitted to the output shaft 30 through an intermediate member 58 which has tongue and groove connections with the pinion 46 and the out-put shaft 30 pinion 46 has a boss 60 which has a groove 62 formed therein to receive a tongue 64 on the member 58. Similarly, the shaft 36 has a flange 66 in which is formed a groove 68 for receiving a tongue 70 on the member 58. Preferably the slots 62 and 68 are disposed in a plane transverse of the axes of the pinion 46 and shaft 30 respectively and lie diametrically of said axes. Preferably the tongues 64- and 70 are disposed at right angles to one another to assure smooth transmission of pinion rotation to the output shaft 30 and furthermore to minimize frictional losses and the like. It will be noted that preferably the axes of pinion 46 and shaft 30 are aligned in this normal operating position to minimize the relative movement between the tongues 64 and 70 and the grooves in which they are received. Such sliding action is inherent in the operation of the integrator as will be later apparent and is maximum when the plate 50 is displaced to the position illustrated in FIGURES 4-6.

As was indicated above, the integrator 28 is adapted to provide a false output feedback signal to the shaft 35} in order to prevent compressor stall, this being done by powering of the actuator 32. It will now be noted that the rod 52, which forms, in part, the support for trunnion 5t and pinion 46, is secured to a piston '72. This piston, in combination with a cylinder 74 secured to the housing 42,

fed through a respectively. More specifically, the

All

forms the actuator 32. The piston '72 is normally maintained in its illustrated position by a spring 76. Upon opening of the valve 36 (FIGURE 1), the piston 72 is rapidly displaced toward the left to a stop position in which the piston 72 bottoms against the cylinder 74. As this occurs, assuming for the moment that rack 44 is stationary, the pinion 46 will rotate in a counter-clockwise direction, which rotation will be imparted to the output shaft 3i as the false feedback signal. So long as the valve 36 is open, the pinion 46 will be displaced towards the left as indicated in FIGURES 4-6, establishing a new reference point about which the guide vanes 12 will be maintained with the mechanical feedback 26 thereafter providing a further feedback control as before. This enables the guide vanes to be further regulated in accordance with parameters other than the condition-causing excessive hot gas ingestion.

FIGURES 4-6 illustrate by darts 78 and 80 on the pinion 46 and flange 66 respectively that a given angular displacement of the pinion 78 will result in an equal angular, or linearly proportionate, output displacement to the shaft 30. It further illustrates that the output rotation of shaft 30 is a direct function of the linear displacement of the mounting plate St It will also be noted that a given linear displacement of the plate 50 will produce the same angular output in shaft 3% as the same given linear displacement of the input member 40 and rack 44, this being due to the fact that in either case the moment arm causing rotation of pinion 46 is the same, namely the radius of the pitch line of the pinion teeth.

As advantageously employed in the described guide vane control system, the present device provides a simple and accurate method for quickly introducing a false feedback signal into the controller 13 to reposition the reference point about which the guide vanes 12 are to be positioned. In doing so, it is, of course, desirable, though not entirely essential, that the rate of movement of the plate 5% have a linear relationshi to the angular rotation of the output shaft 30. However, in other applications of the present integrator this feature is of particular significance in that it can function as a true integrator in which the linear movements of two inputs are algebnaically summed by the angular position of the shaft 30. Thus, assuming that movement of the plate 54 toward the left is a negative direction and toward the right is a positive direction and that movement of the input member 40 toward the left is positive and movement toward the right is negative, clockwise rotation of the output shaft 30 would be positive and counterclockwise rotation would be negative. Thus, the positive input to the plate 50 would result in a given angular displacement of shaft 30 and the same positive input to the member 49 would result in twice the positive output to the shaft 30. Similarly, if an equal negative input were made to the member 40, the angular position of the output shaft 39 would remain constant, providing the input rates were the same.

When employed in the described vane control system, the ability to use two linear inputs to the integrator 28 is a great advantage in simplifying mechanisms. Furthermore, the compactness and simplicity of the present design not only minimizes the manufacturing expenses but also affords an extremely lightweight and reliable mechanical integrator which is particularly desirable for use in aircraft control systems.

It will be apparent that the inputs to the integrator at 28 need not be necessarily from position feedback devices. The integrating mechanism therefore has broader utility in other control systems in which two linear displacement inputs are to be transformed into a rotary output which is directly proportional to the algebraic sum of the direction and displacement and/ or rates of the inputs. Other modifications will occur to those skilled in the art and the scope of the invention is to be derived solely from the following claims.

Having thus described the invention, what is claimed as novel and desired to be protected by Letters Patent of the United States is:

1. A servo mechanism comprising,

means for producing a demand control signal,

a first actuating means positioning an element in response to said demand control signal,

a mechanical integrator comprising,

first and second input members guided for linear movement,

a relatively fixed, rotatable output shaft, disposed transversely to said input members,

a rotary integrating member having rolling movement relative to said first input member in response to -movement of said first input member,

means connecting said second input member and said rotary member for displacing said rotary member laterally relative to said output shaft -for also impanting relative rolling movement between said first input member and said rotary integrating member,

means rotating with and coupling said rotary integrating member to said output shaft throughout the range of lateral displacement of said rotary integrating member,

means displacing said first integrator input member as a function of the displacement of said element, the output shaft of said integrator being connected to said servo mechanism to provide a position feedback signal thereto,

a second actuating means connected to said second integrator input means for producing a fixed input displacement in response to displacement of a second element,

whereby displacement of said second element results in a false position feedback signal from the integrator output shaft and the first element is repositioned in a predetermined amount while said second actuator is so displaced.

2. A servo mechanism as in claim 1 in further combinz tion with a gas turbine engine guide vane control systei for momentarily repositioning guide vanes during a cor dition of abnormal operation wherein,

the controlled element comprises a plurality of sai guide vanes, positioned by the first actuating mean as a function of said demand control signal,

the first integrator input member is displaced as a linea function of the displacement of said guide vanes, said rotary integrating member is normally in align-men with said output shaft,

said rotary output shaft is connected to said signal pro ducing means to provide a feedback signal thereto reflecting the position of the guide vanes, to null ou the demand signal,

the second actuating means, connected to the seconc integrator input means, is responsive to an abnormal engine condition, thereby imparting a fixed displacement to the second integrator input member and a false position feedback signal from the integrator output shaft to the signal producing means to produce a demand signal which repositions the guide vanes during the condition of abnormal operation.

References Cited UNITED STATES PATENTS 1,244,533 10/1917 Morse 6431 2,949,735 8/1960 Stefucza -3929 3,006,145 10/1961 Sobey 60-3929 2,932,255 4/1960 Neukirch 6431 XR FOREIGN PATENTS 1,277,287 10/1961 France.

842,451 8/1960 Great Britain.

JULIUS E. WEST, Primary Examiner. 

